Promises - Part 8 of Functional Programming in JavaScript:https://www.youtube.com/watch?v=2d7s3spWAzo
If you are a JS developer, then you should be already familiar with the concepts from the links above (^^). I'm including the links for other people who want to master the JS. In React we use much more VanillaJS than in other solutions like AngularJS or EmberJS.